Many industrial processes produce waste heat of low temperature, such that little useful work is generally accomplished with this waste heat. It is well known that certain thermodynamic cycles, such as absorption cooling, can provide environmental cooling even from low grade heat sources, such as thermal solar, engine exhaust, and bottoming cycles for industrial steam generators, but absorption cooling suffers from low efficiencies. In addition, cycles, such as absorption cooling, cannot easily integrate electrical power generation.
Prior art has not completely integrated heating and cooling with electrical power generation, or alternatively with an electric motor/generator to supplement the thermodynamic cycle with the electric motor during periods of low thermal energy availability. Furthermore, a self-contained system that includes a prime mover, such as an internal combustion engine, combined with power generation and heat and cooling functions, which are further supplemented by waste heat recovery from the engine exhaust have not been described. In the prior art, some systems use refrigerant as the working fluid to generate electrical power (Edwards, U.S. Pat. No. 4,738,111), commonly referred to as an Organic Rankine Cycle. Other systems provide for power and cooling, but use an external combustor, instead of an internal combustion engine (McCullough, U.S. Pat. No. 5,228,309). Many do not consider the need for recuperation, which transfers the remaining usable heat at the output of the Rankine expander to pre-heat fluid entering the heater or boiler.
Prior art for the apparatus that provides the heating and cooling functions have been well described elsewhere (Benson, U.S. Pat. No. 6,581,384). It can be summarized that none have maximized the efficiency achievable with a combined Rankine and refrigeration cycle. Some approaches either do not recuperate heat from the working fluid (Steuart, U.S. Pat. No. 1,871,244) or do not recuperate heat in a fashion that maximizes the temperature of the working fluid entering the heating device (Brola, U.S. Pat. No. 4,118,934). Some systems attempt to only provide heating (Schafer, U.S. Pat. No. 4,271,679) or cooling (Horn, U.S. Pat. No. 2,875,589) but not both. Some add complexity by using separate working fluids for the power and heat pump cycles (Silvern, U.S. Pat. No. 3,153,442) (Schafer, U.S. Pat. No. 4,271,679).
Hence, there is a need for a single system of sufficient efficiency and simplicity to make the manufacture and operation economically attractive. Since the intent of the system is to operate from external heat source, or be supplemented by recovery of heat from an integrated prime mover, the integrated power, heating and cooling system must be flexible enough to accommodate variable electrical and air conditioning loads and allow simple controls with a minimum of sensors and actuators.
FIG. 1 shows the basic heat driven cooling cycle as described in prior art (Benson, U.S. Pat. No. 6,581,348). As illustrated in FIG. 1, the apparatus is configured for the cooling mode and consists of a working fluid which has a low critical pressure and temperature, such as a common refrigerant, and a liquid pump 47, which pressurizes the refrigerant from an intermediate pressure liquid to a high pressure liquid. The high pressure liquid passes through one or more recuperators, 17 and 14, to become preheated prior to passing to heater 2, where a heat source 1 heats the working fluid. The working fluid passes through the expander start-up and overspeed control valve 8 to expander 9. The working fluid is expanded through expander 9, which may be a turbine, piston motor, or some other device which can extract work from the working fluid. While passing through expander 9, work is extracted from the working fluid. Expander 9 drives a compressor 13 through a common shaft, where a speed sensor 11 transmits the speed of expander 9 and compressor 13 rotating group back to the controller to use in the speed control logic.
The exhaust from expander 9 passes through recuperator 14 and 17, where much of the heat is transferred from the expander exhaust gas to the liquid entering heater 2. Compressor 13, using the same working fluid as expander 9, compresses the working fluid from a low pressure, gaseous state to an intermediate pressure gas as part of a typical refrigeration cycle. The output from compressor 13 is co-mingled with the outlet of first recuperator 14. The combined outlet flows from expander 9 and first recuperator 14 and can then be optionally passed into recuperator 17 to extract as much heat from the working fluid as possible. The working fluid then passes through five-way reversing valve 23 from port 18 to port 20 to condenser heat exchanger 26. In an alternative embodiment, the condenser may be cooled by an externally chilled fluid as would be supplied by an evaporative type chiller.
The working fluid exits condenser 26 as an intermediate pressure liquid and is split, where part of the liquid passes through the bi-directional, variable area expansion valve 37, and the other part of the liquid passes through check valve 32. Upon exiting the expansion valve 37, the intermediate pressure liquid becomes a low pressure liquid. The low pressure liquid enters evaporator heat exchanger 43 to cool a space, such as a building. In an alternative embodiment, the evaporator may be used to cool another fluid, rather than directly cooling a building. The working fluid leaving evaporator 43 is a low pressure vapor and is passed through five-way reversing valve 23 from port 21 to port 22, where the working fluid returns to compressor 13. Port 19 is not used in the cooling mode. The remainder of the working fluid not passing through expansion valve 37 instead passes through check valve 32 and eventually returns to the liquid pump 47. Check valve 33 is checked closed.
In FIG. 2, the apparatus is configured for the heating mode. All functions of the system, unless noted below are the same as in FIG. 1. Differences from FIG. 1 include passing the combined flow from expander 9, after passing through recuperator 14, and the outlet flow from compressor 13 through port 19 of the five-way valve 23 to port 21. Recuperator 17 and port 18 are not used in the heating mode. The intermediate pressure gas from five-way valve 23 leaves port 21 and passes through heat exchanger 43, which acts as a condenser.
The working fluid exits the condenser as an intermediate pressure liquid and is split where part of the liquid passes through the variable area, bi-directional expansion valve 37, and the other part of the liquid passes through check valve 33. The intermediate pressure liquid becomes a low pressure liquid, upon exiting expansion valve 37. The low pressure liquid enters heat exchanger 26, which is being used as an evaporator. The working fluid leaving the evaporator is a low pressure vapor and is passed into port 20 of five-way valve 23 and out of port 22, where the working fluid returns to compressor 13. The remainder of the working fluid not passing through expansion valve 37 instead passes through check valve 33 eventually returns to high pressure liquid pump 47. Check valve 32 is checked closed.